Present invention is related to the mining area, particularly to the pyrometallurgic area, specifically to the smelting and conversion process that occurs in furnaces and converters for production of refined metals when applying a field of mechanical waves in their interior.
Within the mining processes, for example copper, a Converter, the Teniente Converter, used as the sole primary fusion system, has a system allowing injection of dry concentrate through injecting tuyeres, thereby turning it into an autonomous system. The Teniente Converter is the smelter""s most important furnace since it defines its operational cycles. Once the equipment""s operational conditions have been defined regarding concentrate composition, the fusion capacity and kinetics of the process depend on flow and oxygen enrichment of air blown through tuyeres.
The Teniente Converter (basically a horizontal cylinder with an outer mantle or shell lined in its interior with refractory material of determinate thickness within which 1250xc2x0 C. chemical reactions occur, with dry concentrate injecting tuyeres, air blowing tuyeres and a drainage system placed at a certain height over ends of the Converter) is fed with a copper concentrate of approximately 28% copper content, injecting additionally through blowing tuyeres oxygen enriched air that produce a series of reactions that increase copper concentrate until it reaches 75% copper content.
The Teniente Converter operation is based on heat generated by pyritical decomposition and sulphur oxidisation reactions and consists mainly of melting the solid raw materials that are fed into it, oxidise part of the load and obtain as a product two liquid phases, one rich in copper (white metal, of higher density) and another formed basically by oxides present in the bath (slag, of lesser density which remains over the metallic bath or white metal). Additionally, gases rich in sulphur dioxide are generated during the operation, which are sent to the acid plant for treatment. The Teniente Converter delivers as a final product white metal, slag and gases.
The white metal in the Teniente Converter is a liquid solution comprised basically by a mixture of copper and iron sulphides (Cu2S and FeS) and contains additionally a part of the impurities present in the concentrates. Ellimination of these impurities occurs during the subsequent conversion processes.
White metal""s higher density in relation to slag causes the white metal drops to descend through the bath to form a melted metal phase at the bottom of the furnace.
The melt""s slag is formed by oxides fed to the converter; iron oxides produced by FeS oxidisation. Within the types considered the following are found: Fayalite (2FeOSiO2), Magnetite (Fe3O4) Silica (SiO2), Allumina (Al2O3), calcium oxides (CaO), copper oxides (Cu2O) and White Metal (Cu2S) trapped mechanically.
The desirable characteristics for slag are:
Should be miscible with the metal bath (white metal).
Low copper solubility.
Be fluid in order to minimise metal bath, concentrate and particle entrapment, and to allow adequate evacuation through the slag taphole.
The gas is formed basically by sulphur dioxide (SO2), oxygen (O2), Nitrogen (N2) and water steam (H2O).
Today, the process of obtaining white metal by Teniente Converter (CT) operation is subject to several problems whose solution has been attempted by different means. Amongst these difficulties we can mention the lack of online measurement of levels of the different phases. Currently, this measurement is carried out with a rod that is inserted into to the liquid metal thereby locating an operator over the converter, with the inherent risks involved by this technique. Furthermore, another main problem in CT operation is the formation of accretions at ends of air blowing tuyeres that inject oxygen enriched over the bath, since obstruction of airflow consequently decreases the chemical reactions within the converter, thereby decreasing its fusion capacity. Additionally, the accretions adhere firmly to the refractory material and part of this last is removed together with them, producing serious wear due to use of the tuyeres cleaning machine to eliminate the accretions, ultimately producing internal ruptures evidenced at short term by the leakage of material to the exterior.
Furthermore, the slag entraps mechanically as well as chemically, in approximately the same proportions, a significant copper content (around 8%). This copper must be recovered subsequently in a slag treatment furnace with the greater cost involved for the complete process.
In the white metal phase chemical reactions occur due to oxygen injection. These chemical reactions have their own kinetics given by the contact surface between the bubbles and fluid metal that corresponds to the interphase where the chemical reactions occur.
An increase in the chemical reactions means an increase in the production of desired metal in a fixed time period. This has its basis in kinetics, v=kexe2x88x92E/kxcfx86T, where E is the activation energy. In this way, the emission of mechanical, for example sonic, waves speeds up a specific reaction, as it is able to supply a certain amount of energy (activation energy) and control it, meaning also that it is selective.
Specialized literature is aware of the fact that mechanical waves travel through solids as well as liquids and gases. Effectively, application of ultrasound in gases and metals in liquid state at high temperatures behaves like mechanical waves in general (See xe2x80x9cUltrasound Fundamentalsxe2x80x9d Jack Blitz, Alhambra Editorial, 1st Spanish edition of 1969, pages 31-33).
Because of this, present invention employs mechanic wave transmission of certain characteristics to maximise the physical-chemical coupling of different media. Additionally, using the transmission and reflective properties of these mechanical waves that travel through different media (of different densities), it supplies an online and non-invasive measurement of parameters very important for an optimal operation of the process.
Present invention consists of a system for generating mechanical waves, sonic as well as ultrasonic, of specific characteristics, transmitted to the interior of a CT so as to maximise the physical-chemical coupling of different media. Additionally, using the transmission and reflective properties of these mechanical waves that travel through different media (of varying densities), it supplies an online and non invasive measurement of parameters that are very important for an optimal operation of a process.
So, a system has been implemented that increases the kinetics of chemical reactions and in consequence, an increase in the production of metal.
This higher production of metal results from the higher efficiency of oxygen reactions within the metal bath. The reaction capacity of oxygen per unit of volume of the metal bath per time unit in a converter or furnace is measured through the SBSR (Specific Bath Smelting Rate), and is theoretically defined by:
SBSR=exc2x7fxc2x7Qo/VBath
Where: e=efficiency of oxygen consumption; f=oxygen enrichment; Qo=air flow; and VBath=bath volume.
The CT, under influence of the mechanical wave field (for example sonic, ultrasonic or infrasonic) that operates on the metal bath, slag and injected air improves its fusion cycle in terms of an increase in production of metal bath (VBath), in presence of the mechanical wave field.
Additionally there is a quicker homogenisation of the mixture, which stabilises the temperature as well as the density of the mixture, allowing it to approach thermal equilibrium. On the other hand the system eliminates the accretions that form at the ends of the air blowing tuyeres, permitting a relatively constant flow of air to the CT reacting with the higher density fluid, thus extending the operational time of the CT by avoiding the interruption of the process to eliminate said accretions through use of the tuyere cleaning machine that uses sharp tools to do the job.
As a result there is an increase in the useful life of the refractory as well as the CT.
Certainly, another result is the ellimination, to some extent, of the metal entrapped in the slag. The selective attack of the mechanical waves on the different components of the slag inhibits the entrapment of metal by it, thus reducing the quantity of copper trapped mechanically, because said waves deliver enough energy to make the metal drops decant, reducing it greatly.
Another aim of present invention is to provide continuous and discrete on line measurements of temperature and phase levels.
In all industrial processes, the stabilisation of variables is essential for achieving a good process control. In pirometallurgical converters, a good control of the level of the white metal allows to decrease the copper loss due to drag by the slag and also avoids foaming.
Moreover, a good control of the level of slag avoids unnecessary heat loss. Meaning that if we subject converters that contain in their interior fluids of different densities to mechanical waves, these will have different propagation behaviours, and as it is known that their reflection coefficient depends on the media they are transmitted through, the phase levels and the refractory wear can be determined in real time or on line by relating these different reflection coefficients.
On line measurement of temperature of metal bath and slag and eventually of the temperature of the gaseous phase of the CT, allows a constant monitoring of the system, so as to take the corresponding action for a better use of the energy to increase fusion. Additionally it allows to avoid high fluctuations in temperature that produce thermal shock in the refractory. For this reason, the proposed measuring system submits the information directly to the Central Control System of the process in order to execute the programmed operations for each situation.
In the same way, the system detects the white metal and slag levels within certain discrete ranges.